The main objective is to study the structure of viruses with nucleo-proteins and chromosomes. Particular emphasis on the internal organization of their nucleic acids. This will be attempted by using the remarkable optical properties of both DNA and RNA in their various chemical states (charge, single, and double strands, percent of helical structure, etc.). The most important methods will be: a) Optical rotatory dispersion (ORD) circular dichroism (CD) b) Magnetic rotation (Faraday effect) and magnetic circular dichroism (MCD) c) Electric birefringence and dichroism d) Flow birefringence and dichroism e) Fluorescence detected circular dichroism. These methods will give information concerning the following properties: a) The interaction between the bases of the nucleic acids, the nucleic acids and the protein complexes, and the protein coat with itself in the intact virus. b) The interaction properties of the protein coat and the average orientation of the nucleic acid in the virus. c) The hydrodynamic behavior of viruses in solution and the changes in such behavior under alteration of chemical environment. BIBLIOGRAPHIC REFERENCES: Wendel C. Brunner and Marcos F. Maestre, Biopolymers, 14, 555, 1975. Douglas H. Turner, Ignacio Tinoco, Jr., and Marcos F. Maestre, Journal of the American Chemical Society, 96, 4340, 1974. Douglas H. Turner, Ignacio Tinoco, Jr., and Marcos F. Maestre, Biochemistry, 14, 3794, 1975.